Pulsed metal vapour lasers are a class of cyclic pulsed laser which generate high average power at high pulse repetition rates (kilohertz to tens of kilohertz) in the visible and infrared regions of the spectrum. They have been known since 1966 and are utilised commercially in a range of applications, particularly where relatively high power devices are required. Metal vapour lasers producing greater than 120 W are currently available. Such lasers find application in fields such as medicine, forensic science, machining, as pump sources for tunable dyes, and in isotope separation, for example in uranium enrichment.
The active region of a pulsed metal vapour laser is the discharge plasma tube, which is an extended tubular zone in which the metal vapour is confined and through which a pulsed high-current electrical gas discharge passes. The discharge plasma tube is normally formed from refractory ceramic material (usually recrystallized alumina) and surrounded by high-temperature insulation. The discharge plasma tube itself must be maintained at very high temperatures (for example 1400-1700.degree. C. for a copper vapour laser) to ensure adequate vapour pressure (by way of thermal evaporation) of the metal, which is usually distributed along the tube. A buffer gas, usually He or Ne, is invariably present at a pressure of tens or hundreds of millibar to stabilise the metal vapour discharge.
Thus, in operation, metal vapour lasers typically include small pieces of the metal distributed in the plasma discharge tube, and, with the buffer gas flowing slowly through the tube, it is heated externally and/or by the discharge to a temperature such that the vapour pressure of metal in the buffer gas is sufficient to enable lasing to take place. For example, for a copper vapour laser the copper vapour density is typically about 1-10 Pa which requires a temperature of typically 1400-1700.degree. C.
Although previously known metal vapour lasers are typically capable of operating at relatively high efficiencies (up to about 1%) and producing relatively high power output, there is a need for an improved metal vapour laser which provides higher output power than presently known metal vapour lasers, with at least comparable efficiencies, but which is relatively simple to use and is capable of stable operation. Desirably, such an improved metal vapour laser would be capable of operating with no flowing buffer gas.